This disclosure relates generally to heat exchangers and, more particularly, to providing a more uniform distribution of fluid amongst a plurality of parallel, fluid conveying passages of a parallel flow heat exchanger.
Parallel flow heat exchangers include a plurality of spaced parallel passages for conveying a first fluid in heat exchange relationship with a second fluid. A type of parallel flow heat exchanger commonly used as refrigerant evaporators, condensers, and gas coolers in refrigeration and air conditioning applications, as well as used as fluid heating and cooling heat exchangers in other applications, includes a plurality of tubes defining the fluid conveying passages. The tubes are disposed in spaced parallel relationship and open into a common manifold for receiving fluid. Typically, it is desirable that each tube, and even channel for multi-channel tubes receive an equal flow of fluid a fluid chamber within to the manifold into which the inlet end of the tubes open. However, conventional parallel flow heat exchangers, in particular parallel flow heat exchangers having multi-channel tubes, such as mini-channel or micro-channel tubes, suffer from fluid maldistribution, that is from a lack of uniformity in the amount of fluid distributed to each individual multi-channel tube.
Flow maldistribution is particularly problematic in applications where a two-phase fluid is delivered to the fluid chamber of the manifold for distribution amongst an aligned array of the plurality of tubes opening into the fluid chamber of the manifold at spaced intervals along the length of the manifold. For example, in a conventional refrigeration/air conditioning cycle, refrigerant is expanded in an expansion valve and then delivered into the manifold of the evaporator as a two-phase mixture of refrigerant vapor and refrigerant liquid. It is generally accepted that flow maldistribution in two-phase flow heat exchangers may primarily be attributed to the difference in densities of liquid phase and the vapor phase. Additionally, gravity forces may separate the liquid and vapor phases as the two-phase mixture passes along the length of the manifold.
It has been recognized that the maldistribution of the refrigerant flow amongst the tubes of a parallel flow heat exchanger may adversely impact evaporator performance and degrade overall system performance. U.S. Pat. Nos. 8,113,270 and 8,171,987, for example, each disclose the use of an elongated distributor tube inserted within and extending along the longitudinal axis of an inlet manifold of a heat exchanger for distributing a two-phase flow along the length of the manifold.
Although the concept of an elongated distribution tube within the inlet header of heat exchanger has been successful in reducing two-phase flow maldistribution, the need still exists for a two-phase flow distributor and heat exchanger that address the maldistribution of the liquid-phase and the vapor-phase in the fluid flow distribution amongst a plurality of flow passages opening to an inlet manifold of a parallel flow heat exchanger.